(full paper is archived in the Miller Library)
Title: Observations of the oval form of Tectura
(Notoacmea) depicta (Hinds, 1842): Nocturnal cycle on
eelgrass observed in the field and in the lab.
Student Author(s): Dominik, Clare
Faculty Advisor(s): Pearse, John
Pages: 20
Location: Senior Thesis UC Santa Cruz
1996?
Abstract: The sudden apperance of a rare oval form of
Tectura depicta at Del Monte Beach, Monterey Bay, California
has ecologically alarming significance for eelgrass beds (Zostera
marina) in the bay. Not only has this limpet appreared in
densities never recorded before, but it has reduced the seagrass bed
to less than 10% of original coverage since its settlement
(Zimmerman, In Press). Examination of the feeding pattern of T.
depicta both in the lab and in the field began July, 1995 until
March, 1996. Z. marina shoots were collected, planted and
placed in a tank at University of California at Santa Cruz's Long
Marine Lab. Limpets were observed both during the day and at night.
The activity of the limpets was measured by counting how many had
traveled above a designated level from the base of the plant at night
(5cm above the base of shoot=critical level). The same procedure was
done in the field on March 2, 1997 at Del Monte Beach on both day and
night dives. Results clearly suggested that T. depicta had a
nocturnal feeding cycle (chi-squared test of independence
p<<0.001 for both trials in lab, p<<0.001 in the field).
The null hypothesis, that limpet position on the plant was
independent of time of day, was rejected. Though there is a lack of
information on this species it can be postulaed that these limpets
are most active at night to avoid diurnal predators that are visually
cued (Little et al., 1991), (Franz, 1990).